Dual-mass flywheel

ABSTRACT

A dual-mass flywheel comprises a primary mass (7) which is adapted to be fastened to a crankshaft (3) of an internal-combustion engine concentric to an axis of rotation (1) and a secondary mass (9) which is mounted for rotation relative to the primary mass (7) around the axis of rotation (1). The secondary mass (9) is coupled in a rotationally elastic manner to the primary mass (7) by a torsion-damping arrangement (19). The primary mass has two formed sheet-metal parts (35, 37) which define a cavity (47) to accommodate springs (17) of the torsion-damping arrangement (19) and is provided with supplementary masses in order to increase the moment of inertia. The supplementary masses may be made up of extensions (45, 63) of the formed sheet-metal parts (35, 37) or of additionally welded-on mass-rings (67). In particular, the supplementary masses are located in a region which is generally radially outwardly of the secondary mass (9).

This application is a division of application Ser. No. 08/163,134, filedon Dec. 7, 1993 now U.S. Pat. No. 5,471,896.

BACKGROUND OF THE INVENTION

The present invention relates to a dual-mass flywheel for the drivetrain of an automotive vehicle.

A dual-mass flywheel for the drive train of an automotive vehicle, whichis described and shown in DE-A-39 09 892, has a primary mass that isadapted to be fastened concentrically with the axis of rotation to acrankshaft of the internal-combustion engine of the automotive vehicleand a secondary mass which is mounted for rotation around the axis ofrotation relative to the primary mass. The secondary mass is attached toa friction clutch located in the drive train between theinternal-combustion engine and a gear box of the automotive vehicle. Thesecondary mass is coupled in a rotationally elastic manner with theprimary mass by a torsion-damping arrangement.

The primary mass of the previously known dual-mass flywheel is made upessentially of two formed sheet-metal parts. A first part has the shapeof a pan and includes a base wall portion that lies essentially radiallyand is attached to the crankshaft and a peripheral flange portion, whichis joined to the perimeter of the base portion and extends in anessentially axial direction away from the crankshaft. The second formedsheet-metal part of the dual mass flywheel forms a wall that extends inan essentially radial direction and is attached at its perimeter to theflange portion of the first part. Together, the two formed sheet-metalparts define a cavity which is concentric with the axis of rotation andis located in a radially outer region of the primary mass. The cavityreceives the springs of the torsion-spring arrangement.

In such a dual-mass flywheel, the primary mass has a comparativelycomplicated shape, inasmuch as it accommodates the torsion-dampingarrangement in the cavity. If formed sheet-metal parts are used, thedesired shape can be produced in a sufficiently practical manner. It hasbeen found, however, that the flywheel mass of a primary mass made up ofsheet-metal parts is too low for many applications. Consequently,consideration could be given to using thicker sheet-metal for the formedsheet-metal parts; however, on the one hand, this complicatesmanufacture, and on the other hand, it becomes impractical for reasonsof space, in particular because accommodation of the springs of thetorsion-damping arrangement requires a certain amount of assembly space.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a structurally simple andeconomically feasible way of increasing the moment of inertia of theprimary mass of a dual-mass flywheel while still permitting the flywheelto be produced from formed sheet-metal parts.

The foregoing object is achieved, in accordance with the presentinvention, by providing supplementary-mass parts at appropriate placesin the radially outer region of the primary mass. The additional mass isadded to the primary flywheel part without reducing the internalmounting space for the springs of the torsion-damping arrangement.Moreover, the thickness of the components, in particular, of the formedsheet-metal components, may be the same as in conventional, previouslyknown flywheels.

In general terms, the invention is a dual-mass flywheel which includes:a primary mass that is adapted to be fastened to a crankshaft of aninternal-combustion engine in a position that is centered on an axis ofrotation; a secondary mass, which is supported in a manner such that itis rotatable around the axis of rotation, relative to the primary mass,and is adapted to have a friction clutch attached to it; and atorsion-damping arrangement which couples the secondary mass in arotationally elastic manner with the primary mass.

Specifically, the primary mass is composed of two formed sheet-metalparts. A first part is pan-shaped, having a base wall portion thatextends in an essentially radial direction and can be fastened to thecrankshaft and a peripheral flange portion which is joined to a radiallyoutward portion of the base portion and extends in an essentially axialdirection away from the crankshaft. A second formed sheet-metal part isattached to the peripheral flange portion of the first part and, jointlywith the first part, defines a cavity that is concentric to the axis ofrotation and is located in the radially outer region of the primary massand that receives springs of the torsion-damping arrangement.

According to a first aspect of the invention--an aspect that is alsoimportant in the case of primary masses which are not made of formedsheet-metal parts--the primary-mass has in the region near its outerperimeter, a centered, axially extending mass-ring extension into whichthe secondary mass extends (at least partially) in an axial direction.In this case, it is preferred that in an axial direction, the mass-ringextension overlies the external perimeter of a mass-disk of thesecondary mass (which mass-disk functions as the carrier for thefriction clutch). In so doing, one can either vary the mass distributionof the secondary mass (which normally represents the counter-pressureplate of the friction clutch); or else, there is assembly spaceavailable in any event radially outside the friction clutch that can beused for increasing the moment of inertia of the primary mass. Themass-ring extension overlies the secondary mass in an axial direction,preferably essentially entirely.

To the extent to which the primary mass consists of formed sheet-metalparts of the type described above, it is preferable that the secondformed sheet-metal part also take the shape of a pan and have a basewall portion that forms the cavity and extends in an essentially radialdirection, as well as a peripheral flange portion which connects to thebase wall portion radially outward, and extends in an essentially axialdirection away from the crankshaft. The peripheral flange portion of atleast one of the two formed sheet-metal parts--and preferably of bothformed sheet-metal parts--is lengthened axially to make up the mass-ringextension; in other words, the flange portion is extended beyond thedimension required to fasten the flange portions to each other. In sucha design, one can raise the moment of inertia on the primary sidewithout having to change the thickness of the material in the two formedsheet-metal parts. The provision of extensions of the flange portions ofboth parts facilitates manufacture of the flywheel, in particularbecause it permits a mutual centering of the two formed sheet-metalparts by engagement of their peripheral flange portions, and alsobecause the two formed sheet-metal parts can be connected to each other,tightly and rigidly, in a simple manner.

An improvement of the above-mentioned form of embodiment can be achievedif the peripheral flange portion of the first formed sheet-metal parthas a ring-shaped step and has on the side of the step which faces awayfrom the crankshaft a diameter that is greater than the diameter on theside closer to the crankshaft. The step can be used, on the one hand,for the axial positioning of the two formed sheet-metal parts; it ispreferred, however, that a supplementary mass-ring be inserted betweenthe second formed sheet-metal part and the step. The mass-ring isaxially fixed between the step and the second formed sheet-metal part.

While in the form of embodiment described above the mass-ring extensionis achieved by means of integral extensions of the formed sheet-metalparts, one can also provide, in another variant, that the mass-ringextension be made up of a separate mass-ring which is rigidly connectedto at least one of the two formed sheet-metal parts, and preferably toboth formed sheet-metal parts. Such a supplementary mass-ring can serveother functions, over and above its function of raising the mass momentof inertia. In particular, a closed ring may have the ring gear of theengine starter on its outer periphery.

In a preferred embodiment, the mass-ring is centered and welded onto atleast one of the formed sheet-metal parts. Preferably, the extension iscarried out in a manner such that the mass-ring is centered on a ringextension of the second formed sheet-metal part and lies opposite andadjacent to a front surface of the peripheral flange portion of thefirst formed sheet-metal part. In that case, the two formed sheet-metalparts as well as the mass-ring can be attached to each other in a tightand rigid manner, by means of a common enveloping weld seam.

In embodiments in which the starter ring gear is provided on themass-ring, as described above, and the mass-ring is arranged axiallylateral to the primary mass, the assembly space which as a rule is thenavailable in the radial vicinity of the peripheral flange portion of thefirst formed sheet-metal part can be taken advantage of for the purposeof attaching further supplementary masses. For instance, at least oneessentially ring-shaped supplementary-mass element can be attached tothe outer perimeter of the peripheral flange portion of the first formedsheet-metal part. If appropriate, such a ring could also be made up ofring segments, each of which segments is attached, such as by welding,to the peripheral flange portion. The second formed sheet-metal partcan, like the first part, be pan-shaped, such that it has a peripheralflange portion that extends essentially axially with respect to thecrankshaft and axially overlaps the peripheral flange portion of thefirst formed sheet-metal part and, in particular, extends into theperipheral flange portion of the first formed sheet-metal part.

Because of the location of the dual-mass flywheel inserted between theinternal-combustion engine and the primary mass, there will be assemblyspace available in a number of applications that can also be used foraccommodation of supplementary masses. For instance, supplementarymass-rings, in particular disk-shaped rings, can be welded on in theradially outer region of the base wall portion of the first formedsheet-metal part.

According to a second aspect of the invention, which aspect takesparticular advantage of available assembly space in some installations,at least one supplementary mass-ring arrangement is provided within thecavity enclosed by the two formed sheet-metal parts, which ringarrangement is axially and radially fixed to at least one of the formedsheet-metal parts. In this manner, one can, on the one hand, takeadvantage of the assembly space that is available within a portion ofthe cavity, in order to attach supplementary mass-rings or similararrangements. In particular, however, one can, by appropriately shapingthe formed sheet-metal parts, expand the cavity into the assembly spacethat is partially available outside the primary mass and then use thecavity to accommodate the mass-rings. One of the advantages broughtabout by locating the supplementary masses within the cavity providedfor the springs of the torsion-damping arrangement lies in the fact thatthe incorporation of the supplementary masses is achieved more easily.Generally, the supplementary masses that are arranged in ring-shapedfashion within the cavity are retained by capturing them mechanically,such as by utilizing components of the primary mass which are present inany case.

In a preferred embodiment, a ring-shaped bulge which protrudes outwardfrom the cavity is formed in a wall portion extending in an essentiallyradial direction of a least one of the two formed sheet-metal parts,preferably the base wall portion of the first formed sheet-metal part,and the supplementary-mass ring arrangement is installed in the bulgingportion. In this manner, even supplementary-mass ring arrangementswhich, if appropriate, are segmented can be accommodated in the cavity,and it is not necessary to disrupt a closed and more or lesseven-surfaced outer contour of the primary mass. By appropriatelyshaping the bulge, one can achieve a secure fixing of the ringarrangement within the bulge, for instance, by making the bulge with across-sectional inner contour that narrows from the cavity outward, inwhich contour the ring arrangement can be radially fixed by, say, axialbracing. If the bulge is essentially cylindrical in a radially outwarddirection, the centrifugal forces of this region are also securelyabsorbed.

In order to fix the ring arrangement in the bulge in an axial direction,the bulge can be closed at least partially by means of additionalelements, attached (for instance, by welding) to the formed sheet-metalparts. Such an additional element could involve, say, a disk-shapedring; preferably, however, one would choose for such an element asupport plate which is required in any event to support the springs ofthe torsion-damping arrangement; in the conventional manner, the supportplate acts jointly with one of the front ends of at least one of thesprings of the torsion-damping arrangement, which springs areaccommodated in the cavity.

However, fixing the supplementary-mass ring arrangement can also beachieved without such additional elements by means of an appropriatedesign of the bulge, for example, by forming the bulge so that is has anaxial undercut towards the cavity, the supplementary-mass ringarrangement being designed as a radially elastic ring-element which isheld in the bulge by the undercut. To the extent to which the ringelement is slit, it can also be fixed in a circumferential direction bymeans of an axial depression of the bulge, which depression extends intothe slit. In another arrangement, the cross-sectional contour of thesupplementary-mass ring may be made essentially identical to thecross-sectional inner contour of the bulge in order to achieve a maximumincrease of the mass moment of inertia. The matching of thecross-sectional contour can be achieved by appropriate working of thering arrangement, such as by stamping or forging it. In order to achievethe desired contour, the ring arrangement can also be made up of severalindividual parts.

In the case of dual-mass flywheels whose primary mass is built up in theconventional manner out of two formed sheet-metal parts, the formedsheet-metal parts are connected to each other in butt fashion. Accordingto a third aspect of the invention, the region in which the two formedsheet-metal parts are connected is taken advantage of in order to raisethe mass moment of inertia. The peripheral flange portion of the firstformed sheet-metal part (which extends in an essentially axialdirection) or the wall of the second formed sheet-metal part (the latterwall running in an essentially radial direction) make a transition intoan integral, one-piece enveloping bend, in order to form a supplementarymass, said bend abutting against the above-mentioned wall of therespective other sheet-metal part or against an extension of said wall,and being in this region rigidly and tightly connected with the walland/or its extension. Such measures not only make it possible to raisethe mass moment of inertia by means of a simple structural design, butthey also facilitate the centering of the two formed sheet-metal partsagainst each other, particularly if the bend is provided on the secondformed sheet-metal part.

To the extent to which the bend is provided on the second formedsheet-metal part, that bend can face axially away from the crankshaftand/or the base wall portion of the first sheet-metal part, and inparticular, as previously explained, it can extend beyond the outerperimeter of the secondary mass. The bend of the second formedsheet-metal part, however, may also extend towards the base wall portionof the first formed sheet-metal part. In particular, if the bend extendsall the way to the region of the base wall portion, the mass may besubstantially increased in a radially outer region, which greatlyincreases the moment of inertia.

Alternatively, the bend can also be provided on that end of theperipheral flange portion of the first formed sheet-metal part which isdistant from the base wall portion, with the bend extending radiallyoutward. In this fashion, there is created on the primary mass a collarthat protrudes radially beyond the peripheral flange portion and notonly raises in itself the mass moment of inertia but also can haveaffixed to it a supplementary-mass ring. This can be done, for instance,in a manner such that the supplementary-mass ring is placed axiallybetween the collar and a starter ring gear, the latter also being placedupon the peripheral flange portion. If appropriate, thesupplementary-mass ring can be secured against rotating by means ofteeth or the like.

As already explained above, there is often available, in the vicinity ofthe internal assembly space of the dual-mass flywheel, space which canbe put to use by attaching supplementary masses to the outer side of theprimary mass. According to another aspect of the invention, this can beachieved in a particularly simple manner of construction by attaching aring-shaped supplementary mass, concentrically with the axis ofrotation, on the radially outer side of the peripheral flange portion ofthe first formed sheet-metal part (axially lateral to the starter ringgear) or on the outer side of the base wall portion of the first formedsheet-metal part, which base wall portion is adjacent to the outer sideof the crankshaft. In a practical way, the cross-sectional design of thematerial of this supplementary mass matches the shape of the firstformed sheet-metal part. Thus, preferably at least one ring elementdesigned as a disk part is welded to the base wall portion, while atleast one cylinder-shaped ring element is welded to the peripheralflange portion. The ring elements may consist each of severalcircumferentially adjacent segments in a manner such that they allowmanufacture with relatively low material waste. This is particularlytrue for cylindrical ring elements using pre-bent sheet-metal strips.The ring elements may also be designed as closed rings, particularly ifthey are intended for attachment to the first formed sheet-metal part,not by welding but by mechanical locking.

For a better understanding of the invention, reference may be made tothe following description of exemplary embodiments taken in conjunctionwith the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial axial lengthwise cross-sectional view through adual-mass flywheel that is to be arranged in the drive train of anautomotive vehicle; and

FIGS. 2 to 8 are fragmentary cross-sectional views of embodiments of aprimary mass of the dual-mass flywheel according to the invention.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1 shows an axial lengthwise section through the upper half of adual-mass flywheel that is arranged in the drive train of an automotivevehicle. The flywheel includes a primary mass 7 that is adapted to beattached by means of screws 5 to a crankshaft 3 of aninternal-combustion engine of the automotive vehicle in a positioncentered on an axis of rotation 1 of the crankshaft and a secondary mass9 that is mounted for rotation relative to the primary mass 7 around theaxis of rotation 1. The secondary mass 9 includes a secondary disk 11that is supported for rotation by a bearing 13, the bearing beingcarried by a bearing support ring 15, which is attached to thecrankshaft 3 by means of the screws 5. The secondary mass 9 is coupledin a rotationally elastic manner to the primary mass 7 by severalsprings 17 of a torsion-damping arrangement 19. The secondary mass 9carries a friction clutch 21, which is of a conventional design andincludes a clutch housing 25, which is attached to the secondary disk 11by means of screws 23 near the outer perimeter of the secondary disk 11.A pressure plate 27 is supported in the clutch housing 25 in a mannersuch that it is non-rotatable but axially movable and is biased in thedirection of the secondary disk 11 by a clutch mainspring, such as adiaphragm spring 29 supported on the clutch housing 25. The frictionlinings of a clutch disk 33 are fictionally engaged between the pressureplate 27 and a secondary disk 11 which forms a counter-pressure surface.

The primary mass 7 is composed of two formed sheet-metal parts 35, 37,each of which is essentially pan-shaped. The formed sheet-metal part 35has a base wall portion 39 which extends in an essentially radialdirection, which wall in its radially inner region is adapted to befastened to the crankshaft 3 by means of screws 5. A peripheral flangeportion 41 projects from the radially outer region of the base wallportion 39 away from the crankshaft 3 in an essentially axial direction.The second formed sheet-metal part 37 has a wall thickness that is lessthan that of the above-mentioned first formed sheet-metal part 35 andincludes a base wall part 43 that extends in an essentially radialdirection at an axial distance from the base wall portion 39; said wallpart 43 in its outer region also makes a transition into a peripheralflange portion 45 which extends in an essentially axial direction,extending away from the crankshaft 3. The peripheral flange portions 41,45 are connected to each other in a rigid and tight manner, such as bywelding. The two formed sheet-metal parts 35, 37 define in the radiallyouter region of the primary mass 7 a cavity 47 which surroundsconcentrically the axis of rotation 1 and contains the springs 17 of thetorsion-damping arrangement 19. The torque to be transferred by theprimary mass 7 is conveyed by the support plates 49, 51 (which arerigidly connected with the base wall portion 39 and/or the part 43) intothe front sides of the springs 17. A hub disk 55 connected non-rotatablywith the secondary disk 11 by means of rivets 53 forms the output partof the torsion-damping arrangement 19. Arms 57 on the hub disk 55 extendinto the cavity 47 and engage the springs 17. If appropriate, the cavity47 can be filled at least in part with a lubricant or a damping fluid,in which case it is sealed off by a sealing-ring 59 located between thewall part 43 and the hub disk 55.

In operation, the torque generated by the internal-combustion engine istransferred by the two formed sheet-metal parts 35, 37 and the supportplates 49, 51 to the springs 17 of the torsion-damping arrangement 19;the springs transfer it to the friction clutch 21 via the hub disk 55and the secondary disk 11. The vibrational behavior is determined by themass moment of inertia of the primary mass 7, by the mass moment ofinertia of the secondary mass 9, and by the spring characteristics ofthe torsional vibration-damper 19. The vibrating masses of the primarymass 7 and of the secondary mass 9 must lie in a specific range ofratios, if the rotary vibrations are to be sufficiently inhibited, ortransferred into a range of speed-of-rotation (rpm) which is of noimportance to the operation of the automotive vehicle. The flywheel massof the secondary mass 9 is defined, on the one hand, by the mass disk11, by the hub disk 55, and by the components of the friction clutchwhich are connected to the latter; one can only add the clutch disk 31and the components of the gear box to the flywheel effect if the clutchis engaged. For the flywheel effect of the primary mass 7, there areincluded in the first place the flywheel effects of the two formedsheet-metal parts, of the springs 17, and of the starter ring gear 61 onthe peripheral flange portion 41 as well as of the bearing mount 15.

It has been found that the flywheel effect of the above-mentionedcomponents of the primary mass 7 is too small for many applications, ifone wants to use for the formed sheet-metal parts 35, 37 thicknesses ofsheet metal which are sufficiently easy to form and to work. In order toraise the flywheel effect of the primary mass, one must provide on theprimary mass 7 supplementary mass parts, not necessarily required fortorque-transfer and torque-damping. A first supplementary mass is madeup of the peripheral flange portion 45 of the formed sheet-metal part 37and an axial extension 63 of the peripheral flange portion 41, whichoverlaps the peripheral flange portion 45. The extension 63 continuesthe peripheral flange portion 41 on that side of the wall part 43 thatis directed away from the crankshaft 3; together with the peripheralflange portion 45, extension 63 extends axially beyond the outerperimeter of the mass disk 11 and ends radially outwardly of thefriction clutch 21. In this manner, a region radially outwardly of themass disk 11 and of the friction clutch 21 is used for accommodating asupplementary mass of the primary mass 7. The increase in mass providedby the peripheral flange portion 45 and by the extension 63 is achievedwith the same material thickness of the formed sheet-metal parts 35, 37that is in general use and is particularly effective since it is of alarge diameter.

In its region that overlaps the peripheral flange portion 45, theextension 63 has an internal diameter that is greater than that of theperipheral flange portion 41 in the region of cavity 47; in other words,the extension has an axial shoulder or axial step 65 facing the wallpart 43. The axial step 65 facilitates the assembly of the primary mass7 because during assembly, the formed sheet-metal part 37 can lieagainst step 65 while the peripheral flange portion 45 is welded to theextension 63.

A second supplementary mass is created by means of several superposeddisk-shaped mass-rings 67 welded onto the base wall portion 39 of theformed sheet-metal part 35 on the outer side facing the crankshaft 3 ina radially outer region--a region in which a certain assembly space isstill available because of the construction of the engine. In the caseof the disk-shaped mass-rings 67, one can use closed rings. Also usableare mass-rings made up of several segments, such as for instance twosemi-circular arcs, which are put together in segment fashion. Themass-rings 67 raise the moment of inertia of the primary mass 7 withoutthe need to manufacture the two formed sheet-metal parts 35, 37 out of athicker material.

Variants of the dual-mass flywheel are shown in FIGS. 2 to 8 anddescribed below. The variants involve different ways of making theprimary mass out of two formed sheet-metal parts that define a cavity inthe radially outer region of the primary mass as well as ways ofincreasing the moment of inertia of a primary mass built up in thismanner. Components of the variants of FIGS. 2 to 8 which function in thesame manner are designated with the same reference numbers; they aredifferentiated by the addition of a letter suffix. In order tounderstand the design and manner of operation of these components,reference may be made in each case to the foregoing general description.

FIG. 2 shows a variant of a supplementary mass, which is housed insidethe cavity 47g that accommodates the springs of the torsion-dampingarrangement. In a flat bulge 69 which axially expands the cavity 47g inthe region of the outer perimeter of wall part 43g of the formedsheet-metal part 37g, there is arranged a disk-shaped mass-ring 71which, in an axial direction, is fixed between the axial step 65g of theperipheral flange portion 41g of the formed sheet-metal part 35g and theformed sheet-metal part 37g; in a radial direction, the mass-ring 71 isfixed by the extension 63g. Teeth 73, which may be provided on theformed sheet metal part 37g or on the component 35g, secure themass-ring 71 in the circumferential direction. Even though it is anadvantage of this form of embodiment that no additional fastening stepsare required in order to fix the mass-ring 71, nonetheless the mass-ring71 can also be fixed, if appropriate, by partial welding, such as withthe wall part 43g.

FIG. 3 shows a section from the radially outer region of the base wallportion 39a of the formed sheet-metal part 35a, namely a region in whichin FIG. 1 the supplementary mass-rings 67 are arranged. Instead of ringsadded externally of the cavity, here the base wall portion 39a has inthis region a ring-shaped bulge 75 which protrudes towards thecrankshaft and receives additional disk-shaped mass-rings 77. Themass-rings 77 have different radial dimensions so that the inner spaceof the bulge 75 is filled essentially completely. The bulge has aradially outer wall 79 which is essentially cylindrical and a conicalradial inner wall 81, which narrows the inner space axially towards thecrankshaft; the bulge is partially delimited towards the cavity 47a(which contains the springs 17a), by means of the support plates 49hwhich engage the springs 17a. The support plates 49a hold the mass-rings77 in the bulge 75 with axial pre-tensioning, by means of which, due tothe conical shape of the wall 81, the mass-rings 77 are also held in aforce fit in a radial direction. If appropriate, the mass-rings 77 maybe clamped in an axially elastic manner, for instance by means of theirown tension. Since the outer wall 79 is cylindrical, the centrifugalforces of the mass-rings 77 may be absorbed without axial stresses upon,for instance, the support plates 49a which are welded to the formedsheet-metal part 35a. It is clear that here again, the mass-rings 77 maybe made up in segments that are consecutive in the circumferentialdirection. Furthermore, instead of the support plates 49a, one can alsoprovide an enveloping or closure ring for the fastening of themass-rings 77 in the bulge 75.

FIG. 4 shows a variant of FIG. 3, which differs from FIG. 3 in thatinstead of the stepped, disk-shaped mass-rings 77 of FIG. 3, an integral(one-piece) mass-ring 83 of FIG. 4 is provided in the bulge 75b. In thecase of mass-ring 83 of FIG. 4, one can use, for instance, a wire ringor the like whose cross-sectional contour is matched to the innercontour of the bulge 75b by means of pressing or forging. If desired,the mass-ring 83 of FIG. 4 can also be made up of severalcircumferential segments.

FIG. 5 shows a bulge 75c of the base wall portion 39c of the formedsheet-metal part 35c, which bulge 75c has a portion facing the axis ofrotation; that is, in this case, the radial outer wall 79c makes atransition, in the region of the transition towards the peripheralflange portion 41c, into a radially inward protruding segment 84. Thesegment 84 produces in the bulge 75c an undercut 85 which axiallyretains a radially elastic mass-ring 87, the mass-ring being insertedinto the inner space of bulge 75c. Furthermore, the bulge 75c supportsthe mass-ring 87 against centrifugal forces. The mass-ring 87 may be aslit ring, and the slit 89 receives a protuberance 91 that projects awayfrom the crankshaft into the bulge for the purpose of securing the ringagainst rotating circumferentially.

FIG. 6 shows a variant of the primary mass 7d which differs from theprimary mass in FIG. 1 in that the formed sheet-metal part 35d, which isto be connected at its base wall portion 39d to the crankshaft, isprovided, at that end of the peripheral flange portion 41d that isremote from the crankshaft, with a bend. The bend is directed radiallyoutward and forms a collar 93. The formed sheet-metal part 37d, whichdelimits the cavity 47d towards the secondary mass, has a radialextension 95, which extends radially outward its wall part 43d (runningin an essentially radial direction) beyond the diameter of theperipheral flange portion 41d of the formed sheet-metal part 35d. Thetwo formed sheet-metal parts 35d, 37d are connected to each other in theregion of the collar 93 and of the extension 95 in a rigid and tightmanner, such as by welding. The collar 93 and the extension 95 representa first supplementary mass, consisting directly of the material of theformed sheet-metal parts 35d, 37d. Furthermore, there is loosely placedupon the peripheral flange portion 41d, axially between the collar 93and the starter ring gear 61d which is rigidly placed upon theperipheral flange portion 41d, a circumferentially continuous(disk-like) ring element 97 which is held in place axially by the collar93 and by the starter ring gear 61d and is held against rotation byteeth (not shown).

In FIG. 1, the supplementary mass that extends axially and overlapsradially the secondary mass is made up by axial extensions of the twoformed sheet-metal parts. FIG. 7 shows a variant in which only theformed sheen-metal part 35e, which is fastened along its base wallportion 39e to the crankshaft, has a peripheral flange portion 41e whichprojects axially from the perimeter of the base wall portion 39e. Thesecond formed sheet-metal part 37e runs essentially in an exclusivelyradial direction and is rigidly connected with the free end of theperipheral flange portion 41e in a butt connection by welding. On theside of the formed sheet-metal part 37e that faces axially away from theformed sheet-metal part 35e, there is attached, centered on the axis ofrotation, a closed mass-ring extension 99 which has, integrally formedinto its outer perimeter, a starter ring gear 101. By means of a step37e, the mass-ring extension 99 is centered on the formed sheet-metalpart 37e and is welded onto the latter. The mass-ring extension 99extends in an axial direction to such an extent that it radiallyoverlies the outer perimeter of the secondary disk 11e. On the outercontour of the peripheral flange portion 41e of the formed sheet-metalpart 35e, there is welded a cylindrical ring-element 105. For practicalreasons, the ring element 105 consists of pre-curved segments or shells,which can be easily made in a waste-free manner.

FIG. 8 shows a variant of the primary mass in FIG. 7 which differs inthat not only the formed sheet-metal part 35f, which is fastened to thecrankshaft, but also the formed sheet-metal part 37f, which is adjacentto the secondary disk 11f, are pan-shaped. From the radially outerregion of the base wall part 43f of the formed sheet-metal part 37f,which wall part extends in an essentially radial direction, thereprotrudes a peripheral flange portion 45f that extends axially towardsthe crankshaft. The peripheral flange portion 45f engages in aconcentrically matching manner the peripheral flange portion 41f of theformed sheet-metal part 35f and extends all the way to the base wallportion 39f. During assembly, the peripheral flange portion 45f on theone hand, centers the formed sheet-metal part 37f on the formedsheet-metal part 35f, and on the other hand, forms in the radially outerregion of the primary mass 7f, a supplementary mass which is notnecessarily required by the mechanical construction. According to FIG.7, once again a mass-ring extension 99f is provided in the radiallyouter region of the primary mass 7f, which mass-ring extension overlapsaxially with the outer perimeter of the secondary disk 11f and isequipped in one-piece fashion on its outer perimeter with a starter ringgear 101f. The mass-ring extension 99f, centered on the shoulder 103f ofthe formed sheet-metal part 37f, lies with an axial front-surfaceaxially opposite the front end of the peripheral flange portion 41f. Inthis way, an enveloping weld seam 107 applied in this region connectsinto one unit not only the two formed sheet-metal parts 35f, 37f, butalso the mass-ring extension 99f. Such a construction can bemanufactured in a particularly low-cost manner.

The invention claimed is:
 1. A dual-mass flywheel comprising a primarymass which is adapted to be fastened concentrically with an axis ofrotation to a crankshaft of an internal-combustion engine, the primarymass having two formed sheet-metal parts of which formed sheet-metalparts a first formed sheet-metal part has the shape of a pan and has abase wall portion which extends in an essentially radial direction andis adapted to be attached to the crankshaft, and a peripheral flangeportion which is joined to a radially outward end of the base wallportion and extends in an essentially axial direction away from thecrankshaft and of which a second formed sheet-metal part is attached tothe peripheral flange portion of the first formed sheet-metal part andhas a base portion which extends in an essentially radial direction,which base portion, together with the first formed sheet-metal part,defines a cavity disposed concentrically with the axis of rotation in aradially outer region of the primary mass; a secondary mass which ismounted for rotation relative to the primary mass around the axis ofrotation and is adapted to be attached to a friction clutch; atorsion-damping arrangement which couples the secondary mass in arotationally elastic manner with the primary mass and includes springsarranged in the cavity; and a separate mass-ring which is locatedradially outwardly of the perimeter of the secondary mass and is rigidlyattached by a common weldment to both of the two formed sheet-metalparts proximate to the cavity.
 2. A dual-mass flywheel according toclaim 1, wherein the mass-ring is circumferentially continuous and hason its outer perimeter a starter ring gear.
 3. A dual-mass flywheelaccording to claim 1, wherein the mass-ring is centered on a shoulder onthe second formed sheet-metal part, has a first surface facing andforming a portion of a weld site with a surface of the peripheral flangeportion of the first formed sheet-metal part, and a second surfacefacing and forming a portion of the weld site with a surface of thesecond formed sheet-metal part, and wherein the mass-ring and the firstand second formed sheet-metal parts are rigidly connected to each otherwith a common weldment at the weld site.
 4. A dual-mass flywheelaccording to claim 1 wherein the second formed sheet-metal part has theshape of a pan and includes a base wall portion which extends in anessentially radial direction and defines the cavity and a peripheralflange portion which is joined to the base wall portion at a radiallyoutward edge of the base wall portion and extends in an essentiallyaxial direction towards the crankshaft, and wherein the peripheralflange portions of the first and second formed sheet-metal parts engagecoaxially with each other in a telescoping relation.
 5. A dual-massflywheel according to claim 4, wherein the peripheral flange portion ofthe second formed sheet-metal part is positioned radially within theperipheral flange portion of the first formed sheet-metal part.
 6. Adual-mass flywheel according to claim 1, wherein at least onesupplementary-mass element which has an essentially ring-shaped form isaffixed on an outer perimeter surface of the peripheral flange portionof the first formed sheet-metal part.
 7. A dual-mass flywheel accordingto claim 6, wherein the supplementary-mass element is a ring elementwhich is a segment of a cylinder.
 8. A dual-mass flywheel comprising aprimary mass which is adapted to be fastened concentrically with an axisof rotation to a crankshaft of an internal-combustion engine, theprimary mass having two formed sheet-metal parts of which formedsheet-metal parts a first formed sheet-metal part has the shape of a panand has a base wall portion which extends in an essentially radialdirection and is adapted to be attached to the crankshaft, and aperipheral flange portion which is joined to a radially outward end ofthe base wall portion and extends in an essentially axial direction awayfrom the crankshaft and of which a second formed sheet-metal part isattached to the peripheral flange portion of the first formedsheet-metal part and has a base portion which extends in an essentiallyradial direction, which base portion, together with the first formedsheet-metal part, defines a cavity disposed concentrically with the axisof rotation in a radially outer region of the primary mass; a secondarymass which is mounted for rotation relative to the primary mass aroundthe axis of rotation and is adapted to be attached to a friction clutch;a torsion-damping arrangement which couples the secondary mass in arotationally elastic manner with the primary mass and includes springsarranged in the cavity; a separate mass-ring which is rigidly attachedto at least one of the two formed sheet-metal parts proximate to thecavity, is located radially outwardly of the perimeter of the secondarymass, is centered on a shoulder on the second formed sheet-metal part,has a first surface facing and forming a portion of a weld site with asurface of the peripheral flange portion of the first formed sheet-metalpart, and has a second surface facing and forming a portion of the weldsite with a surface of the second formed sheet-metal part, the mass-ringand the first and second formed sheet-metal parts being rigidityconnected to each other with a common weldment at the weld site; and atleast one supplementary-mass element which has an essentiallyring-shaped form and is affixed on an outer perimeter surface of theperipheral flange portion of the first formed sheet-metal part.
 9. Adual-mass flywheel according to claim 8, wherein the mass-ring iscircumferentially continuous and has on its outer perimeter a starterring gear.
 10. A dual-mass flywheel according to claim 8, wherein saidat least one supplementary-mass element is a unitary pre-formed shell.11. A dual-mass flywheel according to claim 8, wherein said at least onesupplementary-mass element is composed of a plurality of preformedsegments of a shell.
 12. A dual-mass flywheel according to claim 8,wherein the second formed sheet-metal part has the shape of a pan andincludes a base wall portion which extends in an essentially radialdirection and defines the cavity and a peripheral flange portion whichis joined to the base wall portion at a radially outward edge of thebase wall portion and extends in an essentially axial direction towardsthe crankshaft, and wherein the peripheral flange portions of the firstand second formed sheet-metal parts engage coaxially with each other ina telescoping relation.
 13. A dual-mass flywheel according to claim 12wherein the peripheral flange portion of the second formed sheet-metalpart is positioned radially within the peripheral flange portion of thefirst formed sheet-metal part.